On January 11, the United States reported a record-breaking 1.35 million new COVID-19 infections, shattering the previous record set just eight days before.
The sky-high case rate—roughly four times higher than the numbers of daily infections seen last January—are a testament to the transmissibility of the Omicron variant.
A highly mutated version of SARS-CoV-2, the virus that causes COVID-19, the Omicron variant has been shown to cause breakthrough infections among the vaccinated thanks to its ability to evade the virus-killing neutralizing antibodies that the body makes in response to getting vaccinated.
In a new study from Beth Israel Deaconess Medical Center, researchers found that cellular immunity—or the production of protective immune cells, such as so-called killer and memory cells—induced by current COVID-19 vaccines provided robust protection against severe disease caused by both the Delta and Omicron variants.
In the study, the team assessed samples from 47 individuals vaccinated with either the Johnson & Johnson or Pfizer-BioNTech vaccines.
They used samples from uninfected individuals who received either the Johnson & Johnson or Pfizer-BioNTech vaccines.
They measured CD8+ T cell and CD4+ T cell responses to the original, Delta and Omicron strains of the SARS-CoV-2 virus after one month and then again after eight months following final vaccination.
The team found that Omicron-specific CD8+ T cell responses were more than 80% cross-reactive with the CD8+ T cell response to the original strain of the virus.
Similarly, more than 80% of Omicron-specific CD4+ T cells demonstrated cross-reactivity, although responses could vary among individuals.
Given the role of CD8+ T cells in the clearance of viral infections, it is likely that cellular immunity contributes substantially to vaccine protection against severe SARS-CoV-2 disease.
This may be particularly relevant for Omicron, which dramatically evades neutralizing antibody responses.
The team says current vaccines still provide robust protection against severe disease and hospitalization due to the Omicron variant despite substantially reduced neutralizing antibody responses and increased breakthrough infection.
If you care about Covid, please read studies about why omicron is spreading so rapidly, and antibodies that can neutralize Omicron.
For more information about Covid, please see recent studies that even symptom-free, people with Omicron are much more likely to spread COVID, and results showing that Omicron can be neutralized by a booster dose.
The study is published in Nature and was conducted by Dan H. Barouch et al.
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